Read
Read[stream]
reads one expression from an input stream and returns the expression.
Read[stream,type]
reads one object of the specified type.
Read[stream,{type1,type2,…}]
reads a sequence of objects of the specified types.
Details and Options
- Possible types to read are:
-
Byte single byte, returned as an integer code Character single character, returned as a one‐character string Expression complete Wolfram Language expression Number integer or an approximate number, given in "E" format Real approximate number, given in "E" format Record sequence of characters delimited by record separators String string terminated by a newline Word sequence of characters delimited by word separators - Objects of type Real can be given in the scientific notation format used by languages such as C and Fortran, as well as in standard Wolfram Language format. A form like 2.e5 or 2.E5 as well as 2*^5 can be used to represent the number
. Objects read as type Real are always returned as approximate numbers. Objects read as type Number are returned as integers if they contain no explicit decimal points. - The following options can be given:
-
NullRecords False whether to assume a null record between repeated record separators NullWords False whether to assume a null word between repeated word separators RecordSeparators {"\r\n","\n","\r"} separators allowed between records TokenWords {} words taken as delimiters WordSeparators {" ","∖t"} separators allowed between words - Objects of type String must be terminated by newlines.
- You can specify any nested list of types for Read to look for. Each successive object read will be placed in the next position in the list structure. A depth‐first traversal of the list structure is used.
- Read[stream,{Number,Number}] reads a pair of numbers from an input stream, and gives the result as a two‐element list.
- Read[stream,{{Number,Number},{Number,Number}}] reads a 2×2 matrix, going through each column, then each row.
- You can use Read to get objects to insert into any expression structure, not necessarily a list. Example: Read[stream,Hold[Expression]] gets an expression and places it inside Hold.
- The first argument to Read can be InputStream["name",n], or simply "name" if there is at most one open input stream with the specified name. Read will call OpenRead to open files with no associated stream.
- Read[File["file"],…] is also supported.
- You can open a file or pipe to get an InputStream object using OpenRead.
- There is always a "current point" maintained for any stream. When you read an object from a stream, the current point is left after the input you read. Successive calls to Read can therefore be used to read successive objects in a stream such as a file.
- Read returns EndOfFile for each object you try to read after you have reached the end of a file.
- Read returns $Failed if it cannot read an object of the type you requested.
- If there is a syntax error in a Wolfram Language expression that you try to read, then Read leaves the current point at the position of the error, and returns $Failed.
Examples
open allclose allBasic Examples (2)
Scope (1)
Read an expression from the file specified by the File object:
Possible Issues (1)
Some streams, like those created by StringToStream, give values greater than 255 for the Byte type:
Text
Wolfram Research (1988), Read, Wolfram Language function, https://reference.wolfram.com/language/ref/Read.html (updated 2016).
CMS
Wolfram Language. 1988. "Read." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2016. https://reference.wolfram.com/language/ref/Read.html.
APA
Wolfram Language. (1988). Read. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Read.html